01 - Bring a large pot of generously salted water to a rolling boil. Add the mafaldine and cook according to package directions, subtracting 2 minutes from the recommended time so the pasta finishes al dente.
02 - Three minutes before the pasta is finished, add the broccoli florets directly to the boiling pasta water. Reserve ½ cup of the starchy cooking water, then drain the pasta and broccoli together in a colander.
03 - While the pasta cooks, warm the olive oil in a large skillet over medium heat. Add the sliced garlic and chili flakes if using, and sauté gently for 1 to 2 minutes until fragrant and just beginning to turn golden, taking care not to brown the garlic.
04 - Transfer the drained mafaldine and broccoli to the skillet. Pour in the lemon juice and scatter the zest over the top, along with a splash of the reserved pasta water. Toss vigorously, adding more cooking water as needed to build a smooth, silky sauce that coats every ribbon.
05 - Sprinkle in the grated Parmesan and continue tossing until the cheese melts and the sauce thickens, clinging to the noodles. Season with salt and freshly ground black pepper to taste.
06 - Divide among warmed plates immediately. Finish with an extra shower of Parmesan and a scattering of fresh basil or parsley if desired.